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4
Map reading notes
Introduction
In the course of 2 or 3 years course, Cand
idates will be exposed to
topographical
maps from
tropical countries
such as Mauritius, Tanzania, Zimbabwe and Jamaica. Many of the
topographical maps of these developing countries show landscapes which are basically
rural
with
some urban settlements in th
e making.
Why use topographical maps for Geo Elective Map Reading?
ü
It is
a large
-
scale map covering a specific area of land on the Earth’s surface.
ü
It
is a very useful kind of map that shows the
topography
of a
n area, i.e whether it is flat,
undulatin
g, rugged or mountainous
ü
on the map, variations in
contour
patterns, various shades of
colour
, use of different
symbols
and
abbreviations
help us interpret the landscape and land use fairly accurately.
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5
The Singapore teachers do not
know
the
map
which t
h
e Cambridge setters
will
us
e
for the setting
of the ‘N’/ ‘O’ level Geography Elective Map Reading questions. However, in the course of
preparing you for exams, we will use the commonly used maps used by the Cambridge to expose
you to different types of que
stions and different map reading skills.
By the end of 2 or 3 years, we will have completed the whole booklet. By then, you will be
expected to be an expert for map reading.
Please refer to Annex 1 for the list of skills that you have to master at the
e
nd of 2 or 3 years.
Elective Geography paper is a very
skill
-
based paper
.
The map reading questions carry
10
marks and found in Section A. It is compulsory. There will be
at most 5 parts to this compulsory
structured
question.
1.
Basic map reading skills
notes
(Revision)
·
The below basic map reading skills are
essential in answering
map reading questions.
·
The hands
-
on will be covered during your map reading practice session.
·
Mastering basic map reading skills will allow us to
extract relevant information
from the
map
(under the assessment objectives)
All topo
graphical
maps must bear the following essentials:
o
a
title
to tell which area is mapped
o
a
scale
which is given as a ratio, or in words or as a line scale
o
a
legend
(reference) to show what the symbol
represent and what the abbreviations are
o
grid lines
for finding locations on the map.
o
Compass
directions
which shows the
north point
(a)
Using Legend
ü
The legend of a
topographical
map is also called the key
or references
.
ü
The legend of a top
ographical map is made up of
symbols
.
ü
Symbols are used on maps to represent all kinds of
human and natural features
.
ü
Symbols are drawn
small
and carry fairly similar
likeness
of what they represent.
ü
Most symbols cover a wide range of
geographical feature
s
such as physical features,
natural vegetation and transport lines.
Functions of each elements
All elements of a map are essential for reading and interpreting maps
Title
Grid lines
Symbols
Legends
Scale
North arrow
For locating places
Represent human
and physical features
Ind
icates what the
symbols represent
For converting map
distance into ground
distance
For measurement
of direction
Elements of a map
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6
REMEMBER
:
Symbols are the easiest to read because all you have to do is to look
at the legend
given.
There are
five
types of map symbols:
·
Point symbols.
These represent
point
-
like
featur
es such as houses, dams and mountain
peaks.
·
Line symbols.
These represent features that occur in lines such as roads, railways and
rivers. Different colours are often used to distinguish between them.
·
Area symbols.
These represent features that cover large areas and are identified with
shading or colouring. Examples are forests, orchards and built
-
up areas of towns and cities.
Often a solid colour is used, such as green to show national parks. In o
ther cases a
combination of colours and symbols may be used, such as blue dots with a solid blue outline
to show a seasonal lake.
·
Abbreviations
.
This
m
ay appear beside other symbols to explain what they are or on their
own
.
Th
ey are employed to indicate types of buildings based on their
functions
.
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7
·
Colour.
This brings out the relief
and features even more vividly.
Common
colours are blue
for water features
(rivers, lakes and seas)
, brown for landsca
pe features, green for
vegetation, and
black
for railways and buildings
or red for
main roads
.
Common mistake
s
of
locating features from the legend
ü
Candidates choose the wrong feature(s) because there are
more than 1 feature
attached in
one symbol.
ü
From
this symbol, Candidates are supposed to deduce that,
Watercourse
Waterfall
Rapids
Dam
ü
Candidates often stumbled when asked to locate features that are not found on the legend.
ü
E.g. Refer to map 8 question 1,
State the six
-
figur
e grid reference of the
view point
overlooking the Victoria Falls National
Park
in the southwest portion of the map. [1]
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8
o
For such feature (e.g. viewpoint), Candidates should pay close attention to the
contextual clues from the question.
o
In this case
, the contextual clue is overlooking Victoria Falls National Park.
§
This will mean that the feature is located near Victoria Falls National Park.
(b)
Using Grid References
ü
Grid lines are used to locate features on a topographical map.
ü
The vertical an
d horizontal grid lines are
numbered
from the origin found at the
south
-
west of
the map.
ü
The
vertical
grid lines as represented by the dotted lines are known as
eastings
.
Properties of eastings
ü
Their
values increase eastwards
.
ü
Their values
are shown on t
he
top and bottom edges
on the map.
ü
The
horizontal
grid lines as represented by the long dashes are known as
northings
.
Properties of
northings
Values are
Northings
Values are
Eastings
Contextual clues
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9
ü
Their
values increase northwards
.
ü
Their
values
are shown on the
left and right edges
on the map.
Note:
ü
There is
a tendency to confuse eastings with northings.
o
Reason: Visually, the eastings, being vertical lines tend to create the impression of
pointing northwards. Hence, they are often mistaken
for northings.
ü
The intersection of an easting and a northing gives the
grid reference
.
ü
There are
4 figure grid reference
and
6 figure grid reference
.
ü
To obtain the grid reference, the easting is read first followed by the northing.
ü
A
4
figure grid reference
gives a
grid square
.
Finding 4 figure grid
references
ü
It is used for
general purpose.
ü
Always begin from the
eastings
, followed by the
northing
s
.
Steps:
1.
Locate the grid square of the particular feature to be found.
2.
Read the easting for the south
-
west of the grid square.
3.
Read the northing for the south
-
west of the grid squa
re.
4.
Simply write the two numbers together, with the easting first.
Finding
6
figure grid
references
ü
It is u
sed for
precise
locations
ü
It pinpoints actual location by involving
the
subdivision
of the eastings and northings
reference into
10
imaginary lines
.
ü
Each tiny square represents 1/100 of the original big (grid) square.
Steps:
1.
Locate the grid square of the particular feature to be found.
2.
Divide the grid square into 10 equal parts along both the northings and eastings.
3.
Number these divisions from 0 to 9
along both northings and eastings.
They are bold in the
below diagram.
13
7
8
9
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10
4.
Mark the
southwest corner
of the feature
that you are locating.
5.
Estimate
how far the feature is from the easting first
using the scale in tenths.
6.
Estimate
how far the feature is from
the northing
using the scale in tenths.
7.
Write
the value for the easting followed by the northing.
N
ote
:
ü
The thi
rd number is part of the easting and the sixth number is part of the northing. These
number
s
refer to the small squares in tenths.
ü
Accuracy of 6 figure grid reference depends on subdiving the parts equally and ensuring that
the (dotted) lines are parallel
to the grid lines.
(c)
Scales
ü
The scale is
ratio
of a given distance on a map to the corresponding distance on the ground
ü
Scales allow you to work out distances between places; how large towns, lakes and forests
are; and what the size of the map area is.
Scale may be expressed in 3 ways:
Representative fraction
Statement
Line scale
12
22
23
Values are Eastings
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
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11
ü
As a
statement
.
E.g. One centimetre on a map
represents
100
000 centimetres on the actual ground
or
One centimetre
on a map
represents one
kilometre on the actual ground.
ü
As a
ratio or representative fraction
. For
example: 1:100
000.
ü
As a
line
scale
.
Reading a line scale
ü
A line
scale is shown as a graduated line.
ü
From the right of the zero mark, the line is divided into whole units (km).
ü
From the left of the zero mark, 1 whole unit (km) is subdivided into 5 sec
tions, with each
representing 200 m. The section nearest to the zero mark is 200 m while the furthest is 1,000
m.
Pointer to note about line scale
ü
Candidates have to realise that the line scale does vary from different topographical maps.
Zvishavane’s
top
ographical
map line scale
Victoria Falls
’s
topographical map line scale
From the above line scales,
Candidates should observe that the subdivision of the line scale found on the extreme left side of
the line scale is different from the 2 maps.
However,
the subunits with each representing 200 m are the same.
Conversion Table:
1
m = 100 cm
1km = 1000 m
E.g. 2 cm on the map represents 1 km on the actual ground.
Steps:
2 cm: 1 km
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12
2 cm: 100,000 cm
(convert to the same unit)
1 cm : 50,000 cm
(Divide both s
ides by 2)
1: 50,000
(Eliminate the units)
Common mistake involving statement scale
ü
Candidates often represent scale in a statement by writing 1 cm represents 1 km or 1000m or
100, 000 cm.
This is mathematically
incorrect
!!!!
Additional points to note
ü
A s
cale of 1:50,000 means that 1 cm on the map represents 50,000 cm or (0.5 km) on the
ground.
o
1:25
000 means 1
cm represents
0.2
5
km or 250
m
o
1:100 000 means 1
cm represents 1
km or
1000
m
ü
When asked to redraw a given map extract to a different scale, you
need to determine what
the new scale is. [Refer to O level Nov 2003 Geography Elective paper Q1(a)]
ü
E.g. For a scale of 1cm representing 0.5 km (1: 50,000) ,
o
Half
the scale is 1 cm representing 1 km (1: 100,000)
o
Twice
the scale is 1cm representing 0.25 k
m (1: 25,000)
ü
The terms ‘large scale’ and ‘small scale’ often confuse people. It is wrong to think that a
large
-
scale map covers a large area and a small
-
scale map covers a small area.
o
In fact, a map scale of 1:100
000 is smaller than a map scale of 1:50
0
00.
o
This is because scale is the ratio of the size of the feature as it appears on a map
compared with its actual size.
o
A topo
graphical map with a large scale
will show far
more
details than a
topographical
map with a
small
scale
.
After acquiring the know
ledge of scales, we can measure
distances
from the map.
Straight line distances
·
Straight
-
line dista
nces are measured using a ruler.
·
The distance measured on the map is then read off the given line scale
or Representative
Fraction.
Steps:
To measure the st
raight
-
line distance between two points on a map,
ü
Place a ruler against the two points
ü
Mark the distance of the two points on the ruler
ü
Place the ruler against the line scale to check the actual distance on the earth’s surface
(ground)
Curved
-
line distance
s
ü
Curved distances can
be measured u
sing a piece of thread / string
.
ü
The distance measured is then placed along the given line scale
or Representative Fraction
to obtain the correct actual distance.
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13
Steps:
To measure a curved distance between two points
on a map,
ü
Place one end of the string on the start point.
ü
Use it to follow the curved distance closely.
ü
Mark a mark on the string at the end of the curved distance.
ü
Straighten the string and place it against the line scale.
Alternatively, to measure actual
distance on the ground is to use Representative Fraction,
be it curved or straight line distance.
E.g. If the distance measured on the map is 4 centimetres and the map has a scale of 1:50,000,
then the actual distance on the ground is 4 x 50,000 = 200,000
cm or 2 km.
How to read the distance using line scale?
Steps:
To read a curved/ straight distance between two points [AB] on a line scale,
ü
Place the measured distance AB against the line scale.
ü
Do not place
AB
starting from the zero mark
.
o
Instead, place
the end of point B on a whole
number scale.
o
Then, place the remaining end that must be less than
1cm on the map
on point 0 (zero)
to read the subdivision of the whole unit.
For instance, the distance of AB is measured by a string as shown below.
ü
Then,
straighten the string.
(d)
Directions and Bearings
Directions
ü
Directions can be indicated in terms of compass points.
ü
On a topographical map, the key compass direction, North, is always given.
ü
From there, we can
estimate
all the other 3 cardinal points are South (S), east (E) and West
(W).
ü
Between each of these 4 main cardinal points is a sub cardinal point
–
North East
(NE),
South East (
SE
), North West (
NW)
and South West (
SW)
o
These sub cardinal points
begin
with
North
or
South
and
end
with
East
or Wes
t
.
2.8 km
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14
ü
Between these 4 sub cardinal points are 8 other subsidiary points
–
North North East (NNE),
East North East (ENE), East South East (ESE), South South East (SSE), South South West
(SSW), West South West (WSW), West North West (WNW) and North North West
(NNW).
o
The subsidiary points
begin
with
4 basic cardinal points
and
end
with
4 sub cardinal
points
.
Summary of directions
ü
Cardinal points are shown by the directional indicator.
ü
In many cases, directions are only
approximation.
ü
Each of these
com
pass directions has an equivalent compass bearing.
o
E.g. North East is 45°, North North East is 22½ °.
ü
On a topographical map, a required location is always given from the
observer’s point of
view
.
o
This is indicated by the word
‘from/ of ’
used in the map
reading question
Directions
4 Cardinal points
(N, S, E, W)
4 sub
-
Cardinal points
(NE, NW, SE, SW)
8
subsidiary points
@
Begin with 4 cardinal
points
@
End with 4 sub
-
cardinal
points
(NNE, ENE, ESE, SSE, SSW,
WSW, WNW, NNW)
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15
Measuring Directions
Steps:
To measure the
direction
of one feature or place [A]
from
another [B],
ü
Draw a straight
-
line connecting them [A and B].
ü
At [B], draw a vertical line that is parallel to the eastings of the map. This line indi
cates north.
ü
Look at [B] and use the 16 point compass to describe the position of [B] from [A].
Bearings
ü
It is measured in
angular
directions marked on a magnetic compass
ü
It is
measured clockwise
from 0° to 360°, i.e. a complete circle
ü
It is expressed in
degrees
.
ü
It is
always measured from
grid north
–
referred to as grid bearings
ü
Bearings are compass directions and they have the advantage of being able to give an exact
direction of one place or feature from another.
Measuring Bearings
ü
It is
always taken
from
one point to another
-
from the
observer to the
object
.
N
N
NE
N
E
E
N
E
E
ESE
SE
SSE
SSW
SW
WSW
W
WNW
NW
NNW
S
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16
ü
A
protractor
is used to calculate the actual angle or bearing observed
Steps:
To measure the bearing of one feature or place [A]
from
another [B],
For bearings less than 180
o
,
ü
Draw a straight
-
l
ine connecting them [A and B].
ü
Place the centre of a protractor over the first point [B]. The 0
o
on the protractor must point to
the north.
ü
Read the bearing off the protractor where the line you have drawn cuts its outer edge.
For bearings
more
than 180
o
,
ü
Draw a straight
-
line connecting them [A and B].
ü
Place the centre of a protractor over the first point [B]. The 180
o
of the protractor must be
pointing to the north.
ü
Read the bearing off the protractor where the line you have drawn cuts its outer edge
.
ü
Remember to add 180
o
to the get the bearing of [A] from [B].
Common mistakes
:
ü
Students often stumbled on which
direction
to decide especially to make decisions between
North East and North North East, etc when it is asked in map reading questions.
·
One
possible solution is to find the
bearing
instead of the direction first.
ü
Students should avoid using short forms in direction like NE to represent North East.
E.g. In order to make a rationale choice,
do note that
ü
For answer that involves North North Eas
t, the bearing is less than 22½
o
.
ü
For answer that involves North East, the bearing is more than 22½
o
but less than 45
o
.
NB
: Directions are used to locate the
boundary
where a feature is found.
E.g. Explain the distribution of the agricultural activities
south
of northing 80.
29
15
15
29
96
75
80
S
N
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17
Given that a topographical map has a range of northings between 75 and 96 and a range of
eastings between 15 and 29, candidates should explain the distribution of the agricultural
activities bounded betwe
en northings 75 and 80 and eastings 15 and 29
. This is represented by
the shaded region.
(e)
Heights
ü
Heights of relief features are shown on a map through:
o
Contours
o
Spot heights, trigonometrical station and benchmarks
.
ü
The unit of
measurement given in the legend of the map is usually in
metres
.
Contours
Basic concepts on contours
ü
A contour is a line that joins places of the same height above sea level.
ü
It is represented in
brown
lines on the topographical maps.
ü
The
height
of the c
ontour is indicated on each contour line.
ü
The difference between one contour line and the next is called contour interval.
ü
If only certain contours are numbered, you have to find how many contours lie between the
numbered contours and work out the contour
interval.
ü
A contour interval is given on the l
egend on the topographical maps.
ü
From the below legend, it can be deduced that the contour interval is 20m.
ü
Note: It is possible for two sets of contour intervals to be used, one
for contours below a
certain height and one of those above a certain height.
ü
The height of a point can be given accurately only if it lies on a contour line. If not, we will
have to use approximation.
ü
The height of a feature between two neighbouring conto
urs is estimation. If it is halfway
between one contour numbered 50 m and another numbered 100 m, its height is 75m.
Some pointers to note
:
ü
Contour lines can be confusing to the untrained eye. Thus, trace the contours carefully.
Example:
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18
From the above contours, Candidates should deduce that
point
o
A is 960 m.
o B
and D
are 940 m.
o
C is approximately 950 m.
§
Reason: It is in between point A and D.
ü
Contour lines do not cross one another, but they may be so close together that they almost
merge
into one.
Uses of contours
1.1
The
spacing
(density)
of the contours indicates the
slope
(gradient)
of the land.
§
Contour lines that are close together denote steep slopes.
§
Contour lines that are
far apart
denote gentle slopes.
§
When there are no contour lines, it means the land is almost flat.
§
When the contour lines
spaced
further apart
as the height of the slope
increases
,
the
sl
ope is
convex
.
·
From
low
altitude to
high altitude
:
Steep
à
Gentle
§
When the contour lines
spaced
closer together
as the height of the slope
increases
,
the
slope is
con
cave
.
(broad spacing
à
narrow spacing)
·
From
low
altitude to high altitude
:
Gentle
à S
teep
1.2
Each feature or
landform
is represented by a specific
pattern
of contour lines.
92
0
94
0
96
0
A
B
C
D
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19
Trigonometrical station
.
630
ü
It is represented on a map by a triangle with a dot inside and the height printed beside it.
ü
This shows the
peak
of
landforms
such as mountains or hills.
Spot
height
.
1000
ü
It represents the height of a specific point on a map.
ü
It is taken at random heights by surveyors.
ü
It is symbolised by a dot with the height printed next to it.
ü
A spot height is not marked on the actual grou
nd.
Benchmark
.
ß
970
ü
It represents the height of the place above sea level on a map.
ü
It is measured heights indicated along roads.
ü
It is represented by a dot with an arrow pointing towards it.
ü
The height is printed beside this symbol.
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20
Common mistakes
:
ü
Candidates choose the wrong height from the trigonometrical station/ spot height /
benchmark.
E.g.
In Victoria Falls topographical map
ü
At region A, the height of the trigonometrical station is 940.5 m and not 527 m. This is
because ‘527/F’ has an
alphabet attached to the trigonometrical station.
ü
At region B, the height of the trigonometrical station is 941.7 m and not 528 m. This is
because ‘528/T’ has an alphabet attached to the trigonometrical station.
(f)
Gradients
ü
It refers to the angle of a slope
and it is used to gauge how steep or gentle the slope is.
ü
The
gradient between two places is often expressed as a ratio.
ü
It is a ratio of a vertical distance to a horizontal distance covered between two points of
reference.
Steps:
To calculate the gradie
nt between A and B,
ü
Calculate the vertical distance by finding the difference in height between the two points [AB]
o
The vertical distance will be in
metres
as heights are given in metres.
o
The difference in height between two points [AB] is
measured from t
he following:
§
Trigonometrical stations
§
Benchmarks
§
Spotheights
§
Transport network by
contours, trigonometrical stations, spot heights,
benchmarks
·
(e.g. railway, wide tarred, narrow tarred, gravel road)
§
Any features by
contours, trigonometrical stations, spot
heights,
benchmarks
ü
Calculate the horizontal distance by finding the
straight
-
line distance
between two points
[AB] unless the two points [AB] are along the same track, railway or river.
o
The horizontal distance is the
actual ground distance
on ground
and
not
measurement on
map
.
o
It must be measured in
metres.
ü
Use the following formula to calculate the gradient.
A
B
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21
OR simply,
ü
Since gradient is usually expressed in ratio as 1: x, we divide the horizontal distance by
vertical distance to find the value o
f x. The value of x should
be expressed
in whole numbers.
Comparing gradient
E.g. 1: 5 and 1: 50
1: 5
(not drawn to scale)
1: 50 (not drawn to scale)
ü
A gradient of 1: 5 is steeper than the gradient of 1:50.
Reason: A gradient of 1:
5 has to cover less distance on the actual ground for 1 unit increase in
height. Thus, it is steeper.
ü
A gradient of 1: 50 is gentler than the gradient of 1:5.
Reason: A gradient of 1:50 has to cover more distance on the actual ground for 1 unit increase i
n
height. Thus, it is gentler.
NB: Gradient is
not the same
as scale even though they are expressed in
the same unit
.
*
Intervisibility
*This topic is not covered in your syllabus. However, the concepts involved in Intervisibility can be
asked
in map readi
ng
questions
.
ü
Intervisibility between two points on a map refers to whether or not an observer at point A can
see another person at point B, assuming that there are no tall trees, poor weather conditions
or other obstructions in the way.
ü
Intervisibility is
a theoretical concept.
o
We are interested in determining whether there is any higher ground between them that
may cut off their view of each other.
ü
The best way of testing intervisibility on a topographical map is to see if
(i)
there is any higher ground bet
ween two points
OR
(ii)
the slopes are concave or convex.
ü
From the contour map below,
1 cm
5
cm
1 cm
50
cm
distance) l(Horizonta [AB] points two between Difference
distance) (Vertical [AB] points two between height in Difference
Distance
Height
Tan YS
22
o
Point A and B are intervisible as the slope is
concave
.
o
Point A and C are not intervisible as the slope is
convex
.
o
Point B and C are not intervisible as they are
blocked
by a
hill peak
at
A .
In general,
ü
There is
no intervisibility
between a spot at the bottom and a spot at the summit in a
convex
slope.
·
Reason: The line of sight is blocked.
ü
There is
intervisibility
between the lowest and highest points of the
concave
slo
pe.